[Radiance-general] rtrace values too low compared to 3-phase method

[Greg Ward]

Hi Marouane,

Which version of Radiance are you using?  (I.e., what does "rtrace -version" say?)

There are difficulties finding transmitted solar radiation through unproxied BSDF materials before the 5.1 release.  The latest release adds a new calculation called "peak extraction" that attempts to identify strong peaks in the BSDF view component that it treats separately.  The solution is not perfect, but it generally leads to more correct results in such cases.

Another approach if you are starting from a geometric description of your fenestration and using genBSDF is the +geom option, which includes the system geometry in the XML file.  You can then apply "pkgBSDF" to translate this geometry and surround it with appropriate proxy surfaces, so that your rays will pass through and generate the correct patterns on your interior surfaces, as well as giving you a correct view through the fenestration system.

If you are using genBSDF, what options did you include?  How did you describe the actual BSDF surface(s) in your model?

Best,
-Greg

> From: Marouane.Boudhaim at ise.fraunhofer.de
> Date: December 8, 2017 8:08:22 AM PST
> 
> Hello, 
>   
> I’m trying to calculate vertical illuminance with 3-phase method and validate it against rtrace results.  My results are very different. 3-phase method has illuminance values two order of magnitudes higher. I can only see the the direct solar illuminance on the floor. I suspect that my rtrace command fails to find the sky, because of the complexity of the geometry of my fenestration system. I was wondering if anyone here has already had such a problem in the past with rtrace giving too low illuminance values. 
>   
> My CFS geometry consists of uniformly spaced boxes of 5 cm (picture in the end). The gap between the boxes allow 4%  normal transmittance (tested with 20% too and it’s still dark, 30% start giving some light). 
> Here are the parameters used to calculate the vertical illuminance (and which I suspect may be wrong) 
>   
> 1st way : 3PM : View matrix of the picture (on which I use evalglare to get the vertical illuminance) :  -n 35 -ab 10 -ad 65536 -lw 1.52e-5 -c 9 
>   
> 2nd way : Vertical illuminance with rtrace :  rtrace -h -I -n 40 -ab 10 -ad 8192 -ar 1024 -as 4096 -aa 0.1 
>   
> 3rd way : Rtrace picture (I use evalglare on it) :  rtrace -n 40 -ab 5 -ad 512 -ar 128 -as 256 -aa 0.15 -dc 1 
>   
> Needless to say I made the parameters vary many times before contacting the mailing list, but there are so much parameters and simulation times increase a lot (I mainly increased ab and ar). I have already tried the parameters on the old and new 3pm/5pm tutorials to be sure my 3-pm results are not wrong. Has anyone else had similar experience with rtrace and know how to solve it ? 
>   
> Sincerely, 
> Marouane. 
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